A radio device according to prior art with duplex function and utilizing time or frequency division duplex (FDD, Frequency Division Duplex: TDD. Time Division Duplex) comprises several RF and IF filters both on the transmitter and the receiver side. FIG. 1 shows a TDM radio according to prior art. The radio device 10 comprises on the receiver side a band-pass filter 12 with its input port connected to the antenna switch 14. The output port of the filter is connected to a low noise amplifier (LNA) 17, which amplifies the received radio signal. After this there is a second band-pass filter 18, which further filters the received signal. The output port of the filter 18 is connected to a mixer 11, in which the received signal is mixed with the first injection signal from the synthesizer 22. The intermediate frequency (IF) signal obtained as the mixing result is then supplied to the RF circuit for further processing.
The transmitter section of the radio 10 comprises a second local oscillator (LO) signal 26, which is generated by the transmitter front end (not shown) and mixed in a mixer 30 with the first injection signal. The output of the mixer 30 is supplied to the band-pass filter 13 )which is located before the power amplifier 14 of the transmitter. The output of the power amplifier 14 is connected to the input to a low-pass or band-pass filter 15, so that undesired components can be filtered from the transmitted signal before it is broadcast via the antenna. Between the power amplifier 14 and the band-pass filter 15 there is often a directional coupler (not shown) with which it is possible to measure the power level of the signal going to the antenna.
It is very difficult to integrate two successive RF blocks (e.g. LNA 17 and the antenna switch 14) and the "off-chip" filter 12 between them. The filter may be for instance a helical, a dielectric or another corresponding filter, and regarding the function of the shown radio design 10 it is necessary to use this filter. The difficulty is primarily due to the fact that if the "off-chip" filter and the RF blocks are integrated on the same chip, then the large size of the filter requires large size connection strips--compared to the RF blocks realized in IC technology, whereby the selectivity of the filter is impaired by the electrical stray quantities and inductive coupling caused by these strips. In practice a complete integration will not be economical when "off-chip" filters are used between the RF blocks. Thus TDNI radios according to prior art comprise several RF blocks realized with concentrated or discrete components, and filters connected between the blocks.
50 .OMEGA. was established as a standard impedance in the interfaces between the discrete components and the filters. Manufacturers of filters and semiconductors adapt their input and output impedances to the standard value in order to facilitate a modular design. Very often the input and output impedances of RF circuits would preferably be lower, for instance an optimal input impedance level of the LNA 17 would be about 10 .OMEGA.. The adaptation to the standard value must be made with a matching circuit, which is made of discrete components or which the semiconductor manufacturer integrates as a part of the RF circuit. In order to be able to substantially decrease the size and price of the radio device from the present level we must develop a radio architecture which enables an easier integration of said blocks.
It is known to integrate all active components of a radio transceiver on one chip. The patent publication WO 93/14573 shows a new architecture solution based on time division multiple access and using time duplex. In the architecture presented in the publication all active components of the transceiver were integrated in one circuit, whereby it was possible to increase the degree of the integration. However, the filters essential for the function of the structure are left outside the integrated circuit, so that there are substantial problems in the matching of these circuits.
The major disadvantage of the design presented in the publication is that without a separate duplexer it can not be used in systems using Time Division Multiple Access and Frequency Division Duplex (TDMA/FDD). which in practice almost doubles the physical size of the circuit shown in the publication. Also, the design does not contain any directional coupler or a direct measuring connection for automatic gain control. The directional coupler must be realized as a transmission line outside the integrated circuit, directly on the printed board of the telephone, which is very susceptible to electrical interference. A directional coupler made on the printed board requires a substantial area on the printed board and also causes an extra attenuation of at least 0.5 dB in the transmitter chain which has a direct effect on the power consumption of the telephone and thereby on the achievable talk time.
Another disadvantage of the design presented in the above publication is the poor selectivity of the transmission line resonator filter formed in the ceramic surface. The filter is used to filter the mixing results of the mixer in the transmission branch. Its pass-band attenuation level is low enough, but when low intermediate frequencies of the magnitude 70 MHz are used, then the selectivity is not at all sufficient if we require e.g. 30 dB attenuation level for the mixing results.
Further we know in the prior art a transceiver, in which the duplexer, the transmitter and the receiver are integrated on one chip. This solution is presented in the patent U.S. Pat. No. 4,792,939. In the design according to the patent the duplexer is realized with Surface Acoustic Wave (SAW) filters. This design integrates the receiver's low noise amplifier (LNA), the band-pass filter realized with the SAW technology, and the mixer. The patent further presents a solution in which circuits required by the power control are integrated in said design, i.e. the directional coupler and the control unit, the power amplifier of the transmitter, and the separate amplifier for its control.
The problems of the solution presented in the patent relate to the SAW filters used. The require matching circuits that are large compared to the filters, which make it impossible to apply the solution in mobile phones, and the matching circuits realized as transmission lines on the printed boards are susceptible to electromagnetic interference. The modest power capacity of the SAW filters prevents a duplexer assembled comprising these filters to be used in the transmitter branch of a mobile phone, where the power capacitor may be 2 W. A SAW filter is also very susceptible to temperature changes, which will appear as a frequency drift. This must be observed so that the SAW filter pass-band is made wider then needed, which for its part also prevents the use of these solutions particularly in future mobile phone networks, where the transition band between the transmit and receive bands is made narrower than the present one; for instance in the future E-GSM network, which is a GSM system enhancement according to the ETSI (European Telecommunications Standards Institute) specification 05.05 "European digital cellular telecommunication system (phase 2); Radio transmission and reception", the transition band is only 10 MHz. There should also be mentioned the high passband attenuation of the SAW filters, about 3.0 to 4.0 dB, which is quite too high regarding the transmitter branch of a mobile phone.
Time division multiplex/multiple access (TDM/TDMA) is generally used in digital data communications networks, where the transmission and reception is made in different time slots. If the transmission and reception frequencies are the same, a mobile phone uses an antenna switch to separate the signals, whereby the switch connects the antenna alternately to the transmitter and the receiver branches of the device. As the isolating unit we can use a filter like the duplex filter used in analog telephones, if the transmission and the reception are made on different frequency bands. The latter alternative will come into question also in systems using frequency division multiplex/multiple access (FDM/FDMA).
A digital radiotelephone using Frequency Division Duplex (FDD) requires also filters besides the above mentioned RF switch, because the input of the receiver must have some selectivity and it must protect the low noise pre-amplifier. At the transmitter output harmonic multiples of the transmission frequency and other spurious transmissions such as minor frequencies must be attenuated. The filters further remove noise generated on the receiver's band by the transmitter chain. The frequencies below the transmission band must also be attenuated with a separate filter. In a system using time duplex, such as the DECT (Digital European Cordless Telephone), separate arrangements must further take care of sufficient attenuation of the spurious transmissions generated during signal transmission towards the antenna.
In the prior art we know solutions where the antenna switch and the filter have been combined in the same structure. The U.S. Pat. No. 5,023,935 uses as a filter two parallel transmission lines, of which the first has one end connected to the antenna. The second transmission line has the first end connected to the receiver and this end can be shorted with a PIN diode. The second end is connected to the transmitter through a reverse biased PIN diode. The use of the diodes and the transmission line provides a sufficient isolation, and some degree of filtering is obtained by using transmission lines with a mutual electromagnetic coupling. However, with this design it is not possible to use high powers, and it has very modest filtering characteristics. A further disadvantage of the design is its large size. It utilizes transmission lines with a length of a quarter-wave, having a length of about 8.5 cm at a frequency of 880 MHz. When other circuit elements are added, the total size of the design could easily amount to about 20.times.100 mm, which is far too much in mobile phones.
The patent Fl 90926 presents a method with which the frequency of a filter realized by transmission line resonators can be changed in a desired way and with high accuracy in a time division multiple access system, both when it utilizes one frequency band and two frequency bands. According to the patent the resonators are arranged in groups between the three ports of the filter, and with the aid of an external control signal the characteristic frequency of the resonators between e.g. the first and the third port or between the first and the second port. The resonance frequency of separate resonators is changed for instance with a method presented in the patent Fl 88442 (U.S. Pat. No. 5,298,873), in which an auxiliary resonator arranged adjacent the main resonator is shorted at one end when required, whereby the characteristic impedance of the design will change leading to a change in the resonance frequency. In the present invention it is also possible to use other known methods to shift the frequency of a resonator and a filter comprising such resonators.
The patent FI 90478 shows how transmission lines in the couplings or matching circuits of the transmitter branch can be used as a pale of a directional coupler. In this way the directional coupler can be moved from the circuit board, which is susceptible to interference and losses, inside the cover of the high frequency filter on a substrate with low loss. Measurements have shown that when we move the directional coupler to be part of the filter we obtain, due to the lower insertion loss, a power saving of about 0.3 dB compared to a conventional circuit board embodiment. SUMMARY OF THE INVENTION
The object of the present invention is to create a combined radio transmitter/receiver design, which is applicable in a digital mobile phone system based on Time Division Multiple Access/Frequency Division Multiple Access Frequency Division Duplex/Time Division Duplex/TDMA/FDMA, FDD/TDD), and which on one hand eliminates and/or reduces the above presented disadvantages of antenna switches based on RF switches or duplex filters, and which on the other hand combines the advantages of the above designs. The object of the invention is further to increase the integration degree of a mobile phone by combining with the antenna switch and filter structure the receiver's low noise pre-amplifier and mixer, and the transmitter's power amplifier, directional coupler and mixer.
The object of the invention is attained by integrating the antenna switch, filter, directional coupler, the receiver's LNA and mixer and the transmitter's PA and mixer within the same entity, in which all parts are assembled on one low loss substrate, and where they are located within a common cover protecting against interference. This entity forms one component on the circuit board of the mobile phone.
Essential in the invention is that active components, which are the receiver's LNA and mixer and the transmitter's power amplifier and mixer, are combined to be a part of the filter structure on the same substrate together with the other components of the filter structure.
The radio transceiver according to the invention is characterized in that a switch means is arranged in the connection of its filter section, the switch operating as the antenna switch of the radio transceiver, and that said filter section, the receiver section of the device, and the transmitter section of the device, form a structural entity, in which said receiver section and said transmitter section are arranged in connection with the switch means and the filter section so that
the supporting structure of the transmitter and receiver sections is the same as the supporting structure of the combined antenna switch and filter section, PA1 the galvanic connections between the parts belonging to the arrangement are realized using said common supporting structure, and that PA1 the transmitter and receiver sections are located within the protective cover, belonging to the filter section and made of electrically conducting material.
The active components can be realized as discrete components as one GaAs circuit, or as a multichip module, which is known per se and belongs to prior art. The inventive idea of the present invention is to integrate the active component realized in said way within the filter-antenna switch-directional coupler-structure, whereby the major part of matching circuits can be eliminated, which matching circuits would match the interfaces of discrete components to the standard value 50 .OMEGA..
This means in the first place the matching, circuits required so far at the input of the receiver's low noise pre-amplifier and at the output of the transmitter's power amplifier. Further all passive components required in the structure can be integrated, e.g. in thick film or thin film technology directly on the circuit board by using the MCM (Multichip Module) technology. Thus we can eliminate discrete modules and the reliability of the whole structure increases, its total weight and size decreases. Further we achieve cost savings in the manufacturing. Rewarding the electrical functions it is essential that parasitic elements are eliminated, which results in electrical circuits operating faster and with a lower total power consumption.